The present invention relates generally to method and apparatus for inspecting the thread portion of a bottle and, more particularly, to an automated method and apparatus for inspecting bottle thread which enables high-speed processing of a plurality of bottles.
Returnable bottles, if they are to be reused by a manufacturer, must be inspected for flaws prior to reuse. Screw-on-cap type bottles are especially susceptible to damage in the thread region. To date, most thread inspection has been performed by human inspectors due to the difficulty of adequately inspecting the entire length of a bottle thread with automated devices.
A typical prior art bottle, as illustrated in FIG. 2, may have a thread portion 12 which consists of four separate "threads" or "leads" 18, 20, 22, 24 arranged symmetrically about the bottle central longitudinal axis AA. In one exemplary glass beverage bottle construction, the outer surface of the neck portion upon which the bottle thread is mounted has a radius, of 1.050 inches. Each of the threads in positioned within a cylindrical region on the bottle neck defined by an upper border 26 and a lower border 28 which are separated by an axial distance of approximately 0.14 inches. Each thread or lead 18, 20, 22, 24 begins at upper border 26 and terminates at lower border 28 and extends at a helix angle of 6.degree. 31'. The thread travel about the circumference of this exemplary bottle is 108.degree. which provides a total length of 0.370 inches for each lead. Each of the leads begins at a point spaced 90.degree. from the next adjacent lead and terminates at a point spaced 90.degree. from the termination point of the next adjacent thread. Each lead has a generally uniform, dome-shaped cross section (not shown) having a radius of curvature at its outer surface of approximately 0.016 inches.
A prior art inspection apparatus 10 adapted to inspect the thread portion 12 of a series of identical bottles 16 (only one shown) is illustrated in FIG. 1. Inspection apparatus 10 includes a bottle conveyor system 30 positioned within a light shielding enclosure 32. The conveyor 30 moves the bottles through an inspection station comprising a triggering light beam 34, at least one flash lamp 36, and a camera 38. When a bottle 16 is positioned directly below camera 38, the bottle neck 14 intersects triggering light beam 34 which simultaneously actuates flash lamps 36 and camera 38. The camera 38 produces an image 40 of the bottle top such as illustrated in FIG. 3. Image 40 includes only a partial image 18A, 20A, 22A, 24A of each bottle thread 18, 20, 22, 24. The partial image consists of an image of the top half of the first circumferentially measured 90.degree. of each thread. The remainder of each bottle thread is obscured from the camera's field of view due to the position of the camera and due to the fact that each of the threads overlap approximately 18.degree. when viewed from above. The lower portion of each bottle thread image 18A, 20A, 22A, 24A is also somewhat out of focus with respect to the upper portion thereof due to the fact that the upper and lower portions of the thread are positioned at different distances from the camera and due to the fact that the camera is positioned very close to the bottle thread, e.g. one inch from the uppermost portion of each lead. An electronic data signal representative of image 40 is analyzed by a machine vision system based upon predetermined criteria for detecting flaws in the portion of the image 40 associated with each thread lead 18, 20, 22, 24. Since the image 18A, 20A, 22A, 24A of each thread lead provided in image 40 is not a complete image, the corresponding data analysis will not detect flaws associated with the obscured portion of each lead.